Answer
set 1
Work Step by Step
set 1: {$(1, 5), (2, 5)$}
set 2: {$(5, 1), (5, 2)$}
Points in a cartesian coordinate plane is usually written in ordered pair $x,y$.
Set 1:
In point (1,5), x=1 while y=5
In point (2,5), x=2 while y=5
Set 2:
In point (5,1), x=5 while y=1
In point (5,2), x=5 while y=2
Thus, the set where x-coordinate is paired with only one y-coordinate is set 1 since it has the same value for $y$.
